There are several known methods of organic waste processing, as well several known systems that include bioreactors, for example those disclosed in: U.S. Pat. No. 6,663,777 A1, 18 Sep. 2003. FR 2614888, 1988. RU 2084515 C1, 20 Jul. 1997. RU 2102468 C1, 20 Jan. 1998. RU 2258686, 20 Aug. 2004. RU 2315721 C1, 27 Jan. 2006. RU 2370457 C1, 20 Oct. 2009. RU 2399184 C1, 20 Sep. 2010. RU 2404240 C2, 20 Nov. 2010. RU 88665 U1, 20 Nov. 2009. RU 110588 U1, 27 Nov. 2011. RU 125995 U1, 20 Mar. 2013.
Known designs and methods for biological waste processing include creation of conditions for microbiological digestion of the substrate (i.e. waste to be processed) using methane-producing anaerobic bacteria in a single or multiple stages. Known approaches further include pretreatment of the substrate, the pretreatment techniques ranging from a simple mixing to fine milling before feeding into the bioreactor.
Traditionally, when preparing the substrate it is initially ground up, then mixed with a fluid and/or additives; then the mix is ground in preparation for feeding into the bioreactor. Mechanical milling and mixing devices are traditionally used in the process of substrate pretreatment for organic waste digestion with further addition of liquid (if necessary) and/or other components with or without heating.
Quality parameters of the raw biomass include (but are not limited to): temperature, the level of exposure to the microorganisms and the like. The biomass in its original state almost always consists of cell groups separated by various membranes and protective layers, so decomposition goes slowly and some cell groups remain un-decomposed after digestion
There is a known method of substrate pretreatment that includes milling and mixing of the raw biomass using mechanical blades in a chamber connected, via perforated plate, to a fermentation chamber of the bioreactor (RU 2084515, 20 Jul. 1997).
In accordance with the RU patent 2370457, 20 Oct. 2009, in order to accelerate the fermentation process when preparing the substrate, the substrate is milled and mixed with additional liquid collected from the wet organic fertilizer drained from the anaerobic bioreactor.
There are known methods of organic waste treatment that include milling and homogenization of the organic waste using electrohydraulic charges as the organic waste travels along the length of the apparatus (RU 2135437, 27 Aug. 1999). There are also known methods where organic fertilizer is produced by means of dispersing of the organic portion of the substrate using hydro-percussive impact on the mixture in a closed loop circulation (RU 2258686, 20 Aug. 2005) or by means of ultrasonic vibration during the aerobic treatment with further magnetic treatment during the anaerobic digestion (RU 2207328, 27 Jun. 2003).
There are further known methods of substrate pretreatment where the mixture is mechanically milled or dispersed in order to break down all oversized particles, to achieve a more homogenous mixture for the bioreactor. It is believed, however, that these methods do not achieve an acceptable quality of mixture for intensive microbiological digestion.
Anaerobic digestion of less than optimally prepared biomass even under appropriate conditions takes significantly more time (as much as 2-3 times more), with biogas output being 50-200% less than in the case of a similar amount of optimally prepared biomass.
There are also known substrate pretreatment without milling (utility model RU 88665, 20 Nov. 2009). The prior art approaches attempted to improve on these systems by providing a substrate pretreatment section of a process line under the utility model patent RU 125995, 20 Mar. 2013 containing a storage hopper and a grinder that accepts large grain-sized substrate, transfer of the ground substrate to the hopper output and loading of the ground substrate from the feeding hopper to the loading-mixing conveyor. This pretreatment of the substrate requires a lot of equipment and also does not provide an optimal quality of mixture.
Mechanical rotary shredders are widely used as grinding and mixing tools for the raw biomass, for instance bladed units comprising a driveshaft installed in the chambers separated by a perforated partition feeding into the acid digestion chamber of the reactor (RU 2084515, 20 Jul. 1997).
In order to increase digestion process efficiency in the pretreatment system under the patent RU 2370457, 20 Oct. 2009 there are additional input feeds for liquid supply to the grinding chamber. This liquid is obtained from the wet organic fertilizer drained from the anaerobic bioreactor.
There is also a known installation for organic waste processing into fertilizers where the mixing, milling and homogenization occur in an electrohydraulic chamber with a row of paired electrodes placed inside (RU 2135437, 27 Aug. 1999). There is also a known biogas unit as disclosed in the patent RU 2102468, 20 Jan. 1998, where the pretreatment is realized with the use of a destructor located between the waste collector and the bioreactor. There are also known installations for organic fertilizer production, as disclosed in the patents RU 2258686, 20 Aug. 2005 and RU 2207328, 27 Jun. 2003, in RU 2258686. The first reference contemplates a rotary hydro-percussion device for breaking down the mixture while it circulates in a closed loop, while the second references relies on an ultrasonic vibration generator for the ultrasonic breaking down the mixture for aerobic treatment.
There is also a known biological waste digestion unit as disclosed in European Patent 1636869, 22 May 2008. There is disclosed a substrate pretreatment system for substrate pretreatment for anaerobic digestion of organic waste. This pretreatment system includes a substrate and water mixing device and a number of ultrasonic radiators for ultrasonic processing located around the bioreactor's substrate access channel. The ultrasonic radiator device corresponds to that described in WO 0335579, 22 Jun. 2000, consisting of a chamber and many ultrasonic transducers attached to the outer wall of the chamber. Sixty modules of 50 kW piezoelectric transducers each resonating at 20 kHz are tightly packed in a grid and form five rings around the chamber, 12 modules per ring.
This method increases the rate of hydrolysis and the release of water-soluble substances from the waste, making these substances more exposed to the microorganisms. However the efficiency of this method is believed to be low as the ultrasonic emitters require much time and energy in order to achieve the desired effect. Therefore the quality of the mixture is not believed to be adequate.
Further improvement of the mixture is still possible so as to increase bioreactor efficiency—the most costly element of biogas production.